While some pretentious folks who badmouth people of their own heritage say it means "goat shit," it has become commonly accepted to mean "of little or no value" and multiple Yiddish to English dictionaries confirm this. No 1st generation American I know has used it to mean anything otherwise.

Someone who chooses to insult strangers instead of astutely sharing their knowledge with those who aren't so fortunate to be as perfect as they are may think they are a mensch, but really their words are bupkis.

NOT

Farshtinkener Jews should be fed bupkis straight from the goat's tochas.

The Urban Dictionary T-Shirt

Also spelled bubkes but still means the same thing. The word Bupkis means 'nothing, zero, having no value'. Also it is said by the television character Dr. Zoidberg on the show "Futurama" since he is a Jewish lobster and this word has a Jewish origin it all makes sense.

Zoidberg: "We've had president Bush for four years and all we got was Bupkis"